Crossing with cornish x... Outcomes?

No good dual purpose birds in my neck of the woods, so I'm back to trying to cross in some extra meet (just another 400g or so on a 16 week old bird).

I just wondered, for those who've done it (crossing cornish x into layers or DP), did it go well, or did you find yourself importing some truly unwanted characteristics? Or did the flock stabilise at a good compromise (weight/laying ability) and you were able to happily keep breeding from offspring?